07 Nov 2018 Story Cities and lifestyles

Invisible air polluting gases revealed by satellite imagery

The Copernicus Sentinel-5P satellite, operational since early 2018, is starting to return high resolution maps of air polluting gases that are invisible to the human eye. Amongst the first images released by mission scientists were plumes of nitrogen dioxide flowing from power plants as well as traffic-choked cities in Europe.

Sentinel-5P, the first Copernicus satellite dedicated to monitoring atmospheric chemistry, carries a single instrument called Tropomi. The Tropomi is a spectrometer that observes the reflected sunlight coming up off the Earth and analyzes its many different colours.

Sentinel-5P is the sixth in a constellation of satellites that are part of Copernicus - an Earth and environmental monitoring programme run by the European Space Agency and the European Union.

The satellite can produce daily global maps of the gases and particles that pollute the air. “While pollution puts the health of millions of people at risk, it is important to understand exactly what is in the air so that accurate forecasts can be issued, and, ultimately, appropriate mitigation policies put in place,” the European Space Agency says.

Specifically, the Sentinel-5P satellite is measuring global levels of the following key trace gases: ozone (O3), sulfur dioxide (SO2), nitrogen dioxide (NO2), carbon monoxide (CO), methane (CH4) and formaldehyde (HCHO), as well as aerosols in the Earth’s atmosphere.

All of these gases affect the air that we breathe and therefore our health. A number of these gases also play a role in climate change.

Infographic by ESA

For example, the stratospheric ozone—high up in the Earth’s atmosphere - protects humans from hazardous ultraviolet radiation coming from the sun, while the ozone close to Earth’s surface can cause respiratory problems.

Other gases such as sulfur dioxide, nitrogen dioxide and carbon monoxide are produced by burning fossil fuels. If inhaled by humans, these gases can severely impact the amount of oxygen entering the bloodstream.

Methane is a gas produced by the burning of fossil fuels and the decomposition of organic materials in landfill sites. It can also originate from the digestion of cattle and other livestock. Besides causing respiratory problems, it is also a potent greenhouse gas with strong climate forcing capabilities.

Besides trace gases, Sentinel-5P will also monitor aerosol particles that are produced by the combustion of fuels, forest fires, desert dust or volcanic eruptions. These particles reduce air quality and affect the climate.

One unique aspect of the mission is that Sentinel-5P can measure pollution emitted by individual cities or parts of a city. This is crucial because the information currently used in emission inventories is compiled largely from statistical information on areas, including industrial sites, population density and traffic. These inventories are usually not updated on a regular basis and are subject to national reporting, which can vary from country to country.


The Copernicus Sentinel-5P satellite shows high levels (highlighted in red) of atmospheric nitrogen dioxide over the Netherlands and the Ruhr area of Germany on 7 November 2017. Photo by the European Space Agency


The Copernicus Sentinel-5P satellite shows sulphur dioxide from the Ambae volcano in the South Pacific Ocean in November 2017. Image by the European Space Agency


Air pollution kills seven million people every year, according to the World Health Organization. As a result, the European Space Agency finds monitoring the air that we breathe is vital.

Free and open data

Data from the satellite, free of charge and open to anyone, will be used by the Copernicus Atmosphere Monitoring Service to issue forecasts and, ultimately, help put mitigation policies in place.

Furthermore, it will open new opportunities for owners of small and medium enterprises as well as start-ups. For instance, the data could allow for the development of air quality and atmosphere-related applications including timely air quality information updates and notifications of high ultraviolet radiation via mobile applications or text messages.

“The Sentinel-5P satellite allows us to see and measure air pollution much more accurately,” says Sean Khan of the Global Environmental Monitoring Air Unit at UN Environment. “This newly available high-quality air pollution data has the potential to improve spatial coverage of air pollution and enable governments—particularly in developing countries—and other stakeholders working on the impacts of poor air quality on human and environmental health to develop effective policies to address the problem.”

Responding to similar concerns about the effects of air pollution, albeit on a smaller scale, UN Environment and UN Habitat deployed low-cost technology in Nairobi, Kenya to assess air pollution levels there.

The ability of satellites like Sentinel-5P to offer detailed visualizations of air pollution may be a vital component of strategies aimed to tackle air pollution, especially in cities.

Breathe Life – a global campaign for clean air

The #BreatheLife campaign, led by the World Health Organization, UN Environment and the Climate & Clean Air Coalition, supports cleaner air initiatives, promotes the use of clean energy and helps cities, regions and countries develop policies and programmes to reduce air pollution.

The campaign currently has 43 members and reaches nearly 100 million worldwide.

The Breathe Life campaign stresses the measures that people can take as communities or individuals (for example, to stop waste burning, promote green spaces and walking or cycling) to improve air quality.